Conventionally, it has been known an electronic device having a temperature detecting element that detects a temperature of a heat generating element mounted on a circuit board. For example, JP 2011-9436 A discloses a circuit board having a conductive pattern on a surface opposite to a surface on which a chip thermistor is mounted. When the temperature of a heat generating element rises, heat of the conductive pattern is conducted to a lower surface of the chip thermistor through a lead made of a copper base. The chip thermistor detects the temperature of the heat generating element.